(1) Field of the Invention
The present invention relates to a method of production of a multichip package module in which rough-pitch semiconductor chips and fine-pitch semiconductor chips in combination are mounted on a printed-circuit board.
(2) Description of the Related Art
Portable electronic devices employ a multiple semiconductor chip package module in which various semiconductor chips are contained on a printed-circuit board. Currently, there is an increasing demand to make the portable electronic devices as small as possible in size. To keep up with this demand, it is needed to increase the board density as much as possible and make the board smaller in size.
In order to facilitate mounting of bare chips on a printed-circuit board in which the bare chips are densely packed, development of a flip-chip bonding technique has become prevalent. By using the flip-chip bonding technique, the bare chips can be easily bonded to the densely packed board, and little space around the board is required. The flip-chip bonding technique is a type of thermocompression connection, and it does not use a soldered joint which causes the problem of a lead (Pb) alloy detrimental to the environment.
FIG. 1A through FIG. 1C show a conventional method of production of a multichip package module.
In the conventional production method, shown in FIG. 1A, an adhesive 3 is applied to locations for bare chips on a printed-circuit board 1 (which will be called the board 1) in an assembly line. The board 1 is transported to a vacuum head 41A in the assembly line. By using the vacuum head 41A, as shown in FIG. 1B, a plurality of bare chips 2-1, 2-2, 2-3, and 2-4 (which are semiconductor chips before mounting) are individually positioned at the locations of the adhesive 3 on the board 1. The vacuum head 41A applies a compressive force to one of the bare chips 2-1 through 2-4 against the board 1 individually, so that the bare chips 2-1 through 2-4 are temporarily attached to the board 1.
After the bare chips 2-1 through 2-4 are temporarily attached to the board 1, the board 1 is transported to a multichip mounting machine 42A in the assembly line. The multichip mounting machine 42A has a plurality of thermocompression heads actuated by springs as shown in FIG. 1C. The thermocompression heads of the multichip mounting machine 42A simultaneously apply heat and pressure to all the bare chips 2-1 through 2-4 on the board 1 for about 100 seconds at a time.
In the conventional production method, the mounting of all the bare chips 2-1 through 2-4 on the board 1 is carried out at the same time by using the multichip mounting machine 42A. The use of the multichip mounting machine 42A in the conventional production method increases a productivity of multichip package modules.
However, the above-described conventional production method tends to cause misalignment of the positions of the mounted chips to the board during the transporting of the board with the bare chips temporarily attached or when the compressive force by the multichip mounting machine is simultaneously exerted on the plurality of bare chips against the board. It is difficult for the conventional production method to ensure a sufficient level of quality of the multichip package module.
Generally, the bare chips to be mounted on a single printed-circuit board include a fine-pitch bare chip (such as a microprocessor chip) and a plurality of rough-pitch bare chips (such as semiconductor chips other than a microprocessor chip) per board. Fine-pitch bare chips have a relatively small pitch between stud bumps, and rough-pitch bare chips have a relatively large pitch between studs bumps. Further, fine-pitch bare chips are expensive, and rough-pitch bare chips are less expensive.
Tolerances of the positions of the bare chips mounted on the printed-circuit board in the multichip package module vary depending on the type of the bare chips. The tolerance for the fine-pitch bare chip is relatively small, and the tolerance for the rough-pitch bare chips is relatively large.
If misalignment of the positions of the mounted chips to the board has occurred, it is very difficult to compensate for the misalignment. Such a module is rejected in an inspection process as a defective product during a testing step. Since the tolerance for the fine-pitch bare chip is relatively small, the stud bumps of the fine-pitch bare chip are likely to be separated from or erroneously connected to electrodes of the board due to the misalignment. This may cause a break or a short circuit in the electric connections between the chip and the board. As a result, the multichip package module yield will be decreased due to the misalignment.
Therefore, when the rough-pitch bare chips and the fine-pitch bare chips in combination are mounted on the board, it is difficult for the conventional production method to prevent the occurrence of misalignment of the positions of the mounted chips to the board so as to ensure a good productivity.
In addition, a single-chip mounting technique using a single-chip mounting machine is also known. In a case of the single-chip mounting technique, the single-chip mounting machine applies heat and pressure to one of the bare chips against the printed-circuit board, and the bare chips are individually mounted on the board. Misalignment of the positions of the mounted chips to the board hardly occurs when the compressive force by the mounting machine is exerted on a respective one of the bare chips. However, the single-chip mounting technique requires a significantly long time to carry out the mounting of all the bare chips on the board since it takes about 100 seconds for the single-chip mounting machine to apply heat and pressure to each of the bare chips.